1. Field of the Invention
This invention relates to a magneto-resistive head used as the reproducing head of a magnetic recording/reproducing device and to a method for manufacturing the same.
2. Description of the Related Art
A magneto-resistive head has received much attention as the magnetic head for reproducing a signal recorded on a magnetic recording medium. The magneto-resistive head is a reproducing head constructed by use of a device called a magneto-resistive device (which is hereinafter referred to as an MR device). The MR device detects the signal magnetic field recorded on the magnetic recording medium as change in the electrical resistance caused by variation in the mean magnetization direction of the MR device by use of the phenomenon that the electrical resistance of a ferromagnetic material will change according to the intensity of the external magnetic field. Change in the electrical resistance of the MR device is detected as the voltage drop or current change caused when a sense current is passed through the MR device.
Since the above magneto-resistive head can supply a large reproducing output irrespective of the relative speed of the head with respect to the magnetic recording medium, it can be adequately used as a reproducing head of a magnetic recording/reproducing device such as a magnetic disk device of small size and large capacity.
However, the magneto-resistive head has a particular problem called Barkhausen noise which is caused by the movement of the magnetic domain wall in the MR device. In order to suppress the above noise, the magnetic domain wall may be fixed or removed, that is, the MR device may be formed with the unimagnetic domain structure. Generally, the latter method is used. Formation of the MR device with the unimagnetic domain structure is disclosed in the article by H. Bajoureck et al. AIP Conference Proceedings No. 10, Part 1, "Magnetism and Magnetic Materials", for example.
In order to form the MR device with the stable unimagnetic domain structure, it is effective to apply a bias magnetic field in the longitudinal direction of the MR device which is intenser than the antimagnetic field (approx. 4 .pi.Ms.multidot.t/w) in the longitudinal direction of the MR device caused by the shape demagnetization of the MR device. In this case, t indicates the thickness of the MR device, w indicates the width thereof and Ms indicates the saturation magnetization. In order to realize the above method, a magneto-resistive head shown in FIG. 1 is proposed (which is disclosed in "Technical Paper of Institute of Electronics and Communication Engineers of Japan" MR86-37, by Shiiba et al, for example). The magneto-resistive head has an MR device 13 formed on a base plate 11 with an insulation layer 12 disposed therebetween. Hard magnetic material layers 15 are respectively disposed on the end portions of the MR device 13 and between the end portions and conductive leads 14 for power supply. A bias magnetic field can be applied in the longitudinal direction of the MR device 13 by magnetizing the hard magnetic material layers 15 in the longitudinal direction of the MR device 13.
Further, a magneto-resistive head shown in FIG. 2 is proposed (which is disclosed in U.S. Pat. No. 4,663,685). The magneto-resistive head has antiferromagnetic material layers 16 formed on the end portions of the MR device 13. A bias magnetic field can be applied to only the areas of the MR device 13 which lie directly under the antiferromagnetic material layers 16 by the exchange interaction (exchange coupling) between the magnetic material layers.
However, in the magneto-resistive head shown in FIG. 1 or 2, it is necessary to additionally provide a member such as the hard magnetic material layers 15 or antiferromagnetic material layers 16 for applying the bias magnetic field and the manufacturing process is complicated. Further, it is necessary to provide a space for disposing the member for applying the bias magnetic field, thereby making it difficult to attain the multi-channel structure which is one of the features of the magneto-resistive head.
In the case of the magneto-resistive head shown in FIG. 2, the following problems occur. That is, the end portion of the MR device 13 will be placed on adjacent tracks of the magnetic recording medium and information of the unwanted adjacent track is detected. For this reason, problems such as occurrence of cross-talk noise and corrosion of the antiferromagnetic material layer 16 are provided in the practical case.